Peripheral neuropathy is a complex of disorders of the peripheral nervous system resulting from damage to the nerve or to the myelin sheath. The damage is long lasting, usually outlasting the injury that initiates it.
Chemotherapy-induced peripheral neuropathy (CIPN) is a common and potential disabling side effect of many cytotoxic drugs. Chemotherapy-induced neuropathy is related to cumulative dose or dose-intensities (Verstappen et al. 2003 Drugs 63:1549-63).
The vinca-alkaloids (e.g. vincristine and vinblastine), platinum-based compounds (e.g. cisplatin) and taxanes (paclitaxel and docetaxel) are amongst the most important drugs inducing peripheral neurotoxicity (Visovsky C. Cancer Invest. 2003 June; 21(3): 439-51), Quasthoff S, Hartung H P J Neurol. 2002 January; 249(1): 9-17. Review). These drugs are widely used for treatment of various malignancies such as ovarian, breast cancer, and haematological cancers (Verstappen et al. 2003 Drugs 63(15): 1549).
Vincristine-driven neuropathy is mainly characterized by motor and sensory insufficiency (mixed type of neuropathy). Whilst the underlying mechanism is not fully understood as yet, it has been described to involve an alteration of anterograde axonal transport, ultimately leading to axonal degeneration. Up to now, treatment of vincristine-driven neuropathy is only palliative, as no efficient therapy has been developed so far.
Currently, CIPN is alleviated by dose reduction, which may compromise the efficacy of the chemotherapy treatment. Patients who already have neuropathic symptoms due to diabetes mellitus, hereditary neuropathies or early treatment with neurotoxic chemotherapy are thought to be more vulnerable for the development of CIPN.
In general, treatment of peripheral neuropathy is symptomatic and has no beneficial effect underlying damage to the nerves (Peltier A C, Russell J W. Recent advances in drug-induced neuropathies. Curr Opin Neurol. 2002 October; 15(5): 633-8). For example, pyridoxine (vitamin B6) is used as a method of nutritional support following peripheral nerve damage, antioxidants (e.g. gamma-linoleic acid, alphalipoic acid, and PKC inhibitors and aldose reductase inhibitors) are used to eliminate toxins which may contribute to peripheral neuropathy, anticonvulsant are used to suppress the pain symptoms. Attempts to prevent vincristine-neuropathy using putative neuroprotective agents such as vitamin B1, vitamin B12, glutamate (Boyle et al. J Pharmacol Exp Ther. 1996 October; 279(1): 410-5), isoaxonine (Le Quesne et al., J Neurol Neurosurg Psychiatry. 1985 September; 48(9): 933-5), gangliosides or nerve growth factor (Hayakawa et al., Life Sci. 1994; 55(7): 519-25. 4; Lewis et al. Exp Neurol. 1993 November; 124(1): 73-88) showed limited success.
Interleukin (IL)-6 is a pleiotropic cytokine that not only affects the immune system, but also acts in other biological systems and many physiological events in various organs. In a target cell, IL-6 can simultaneously generate functionally distinct or sometimes contradictory signals through its receptor complex, IL-6Ralpha and gp130. The final physiological output can be thought of as a consequence of the orchestration of the diverse signaling pathways generated by a given ligand. This concept, the signal orchestration model, may explain how IL-6 can elicit proinflammatory or anti-inflammatory effects, depending on the in vivo environmental circumstances. Elucidation of the molecular mechanisms underlying this issue is a challenging subject for future research (Jones et al. 2001, Heinrich et al. 2003 Biochem Journal 374, 1-20). The functional properties of IL-6 are extremely varied and this is reflected by the terminology originally used to describe this cytokine (Horst Ibelgaufts' COPE: Cytokines Online Pathfinder Encyclopaedia).
The biological activities of IL-6 are mediated by a membrane receptor system comprising two different proteins one named IL-6 Receptor (IL-6R or gp80 reviewed by Jones et al. FASEB J. 2001 January; 15(1): 43-58. Review) and the other gp130 (reviewed by Hirano et al Stem Cells. 1994 May; 12(3):262-77. Review). Soluble forms of IL-6R (sIL-6R), corresponding to the extracellular domain of gp80, are natural products of the human body found as glycoproteins in blood and in urine (Novick et al, J Chromatogr. 1990 Jun. 27; 510:331-7, and Cytokine. 1992 January; 4(1):6-11). An exceptional property of sIL-6R molecules is that they act as potent agonists of IL-6 on many cell types including human cells (Taga et al, Cell. 1989 Aug. 11; 58(3):573-81. Novick et al. 1992 January; 4(1):6-11). Even without the intracytoplasmic domain of gp80, sIL-6R is still capable of triggering the dimerization of gp130 in response to IL-6, which in turn mediates the subsequent IL-6-specific signal transduction and biological effects (Murakami Science. 1993 Jun. 18; 260(5115):1808-10). sIL-6R has two types of interaction with gp130 both of which are essential for the M-6 specific biological activities (Halimi et al., Eur Cytokine Netw. 1995 May-June; 6(3):135-43), and the active IL-6 receptor complex was proposed to be a hexameric structure formed by two gp130 chains, two IL-6R and two IL-6 ligands (Ward et al., 1994; Paonessa et al, EMBO J. 1995 May 1; 14(9):1942-51).
In contrast to the expression of the cognate IL-6R which has a limited cellular distribution (reviewed by Jones et al. 2001), expression of the trans-membrane-spanning gp130 is found in almost all organs, including heart, kidney, spleen, liver, lung, placenta, and brain (Saito et al J Immunol. 1992 Jun. 15; 148(12):4066-71).
In vitro, there are many different examples, which show that IL-6 alone does not induce a specific activity unless the soluble IL-6R is administered. For example, IL-6 induces osteoclast formation in co-cultures of mouse bone marrow and osteoblastic cells, only when combined with the sIL-6R (reviewed by Jones et al. 2001). Also, although many neuronal cells are capable of producing IL-6, they remain unresponsive to stimulation by IL-6 itself. Differentiation and survival of neuronal cells can, however, be mediated through the action of sIL-6R (Hirota J Exp Med. 1996 Jun. 1; 183(6):2627-34, Martz 1998).
The circulating concentrations of sIL-6R (agonist) in normal subjects are relatively high and comparable to those of soluble gp130 of above 10 ng/ml, a natural antagonist of IL-6, (Corbi et al 2000 Eur J Cardiotherac Surg. 18 (1):98-103, Disthabanchong et al. Clin Nephrol. 2002 October; 58(4):289-95). In contrast, the circulating concentrations of IL-6 are about or below 10 pg/ml (Kado et al. 1999 Acta Diabetol. Jun 36 (1-2)67-72, Corbi et al 2000. Thus the effect of IL-6 administration in vivo, alone, without co-administration with sIL-6R in disease may or may not be effective and depends on the concentration of the soluble agonist/antagonist in a particular disease and in a particular location in the body.
Chimeric molecules linking the soluble IL-6 receptor and IL-6 together have been described (Chebath et al. Eur Cytokine Netw. 1997 December; 8(4):359-65). They have been designated IL-6R/IL-6 chimera. The chimeric IL-6R/IL-6 molecules were generated by fusing the entire coding regions of the cDNAs encoding the soluble IL-6 receptor (sIL-6R) and IL-6. Recombinant IL-6R/IL-6 chimera was produced in CHO cells (Chebath et al, Eur Cytokine Netw. 1997, WO99/02552). The IL-6R/IL-6 binds with a higher efficiency to the gp130 chain in vitro than does the mixture of IL-6 with sIL-6R (Kollet et al, Blood. 1999 Aug. 1; 94(3):923-31).
MBP and P0 proteins are normally induced during the final postnatal maturation of Schwann cells, and they are re-induced during nerve regeneration. The IL-6R/IL-6 chimera has been shown to induce the expression of myelin basic protein (MBP) and P0 gene products MBP and P0 RNAs and proteins in cultures of dorsal root ganglia (DRG) from 14 day old mouse embryos (FEBS Lett. 1999 Aug. 27; 457(2):200-4. et al., 1999). In addition, the expression of MBP and P0 was found to be induced by IL6R/IL6 chimera also in cultured tumor cells of neural crest origin. In both cases, the induction of MBP and P0 genes by IL6R/IL6, chimera in normal embryonic Schwann cells precursors and in tumor cells of neural crest origin, is associated with a down-regulation of Pax-3 (Kamaraju et al JBC 2002 277 15132, Slutsky et al. J Biol Chem. 2003 Mar. 14; 278(11):8960-8, Haggiag et al, J. Neurosci. Res. 2001).
The stimulatory effect of the gp130 activator IL6R/IL6 on myelination in vivo was demonstrated in a rat model of sciatic nerve transection. Injections of IL6R/IL6 led to a 7-fold increase of the number of myelinated fibers in the regenerating nerve (Haggiag et al, J. Neurosci. Res. 2001).
The therapeutic effect of recombinant IL-6 alone without the soluble IL-6R in an animal model of diabetes-induced peripheral neuropathy has been disclosed in patent application WO03033015. However, it is uncertain whether IL6R/IL-6 chimera alone or IL-6 alone or together with sIL-6R, are capable of a beneficial effect in peripheral neuropathy caused by chemotherapy. In fact, recombinant leukemia inhibitor factor (LIF), another gp130 activator, was tested in clinical trials for preventing peripheral neuropathy caused by carboplatin/paclitaxel (Davis et al. Proc Am Soc Clin Oncol 22: page 740, 2003, abstr 2976) and the results indicated that LIF was ineffective at preventing CIPN at the doses and regime tested.
Therefore, new drugs/strategies for preventing/treating peripheral neuropathy caused by chemotherapy agents are thus needed.